1. Field of the Invention
The present invention relates to a resin diaphragm for a loud speaker (hereinafter referred to as speaker diaphragm) used for, e.g., acoustic output.
2. Description of the Related Art
In order to have better frequency characteristics, means have been employed in manufacturing speaker diaphragms, first, of increasing the stiffness of their material, second, of reinforcing them by adding structural change thereto, and third, of coating their surface with a damping agent or the like in a certain pattern, for example.
A demand for a high specific elastic modulus E/ρ (E: elastic modulus, ρ: density) is raised to increase the range of piston movement, and a demand is similarly raised for large internal losses for smoothing frequency characteristics. Furthermore, in order to enhance the elastic modulus, materials prepared by mixing polypropylene materials so far exhibiting relatively large internal losses with highly elastic fibers (e.g., glass fibers or carbon fibers) and fillers (e.g., mica for coloring) have often been used in injection molding and sheet forming.
Furthermore, to enhance the stiffness of the speaker diaphragm, techniques have been proposed to provide a rib on the speaker diaphragm or vary its thickness (see Japanese Patent Application Publication No. H10-352627). Furthermore, for better frequency characteristics, a technique has been adopted to coat the speaker diaphragm with a damping agent in a certain pattern (see Japanese Patent Application Publication No. H11-215589).
Furthermore, it is known that a speaker diaphragm with remarkably superior characteristics compared to a conventional polypropylene molded product can be manufactured when polyethylene is used as polyolefin being a speaker diaphragm material, because it increases the elastic modulus while maintaining the internal losses properly (see Japanese Patent Application Publication No. H05-153692).